Conventionally, variable capacitance elements whose dielectric constant is changed by a control voltage are proposed by Patent Literatures 1 and 2, for example. These variable capacitance elements adopt a laminated structure (i.e., an MIM structure) of a metal, a ferroelectric material, and a metal, and are provided with a ferroelectric thin film so that a large amount of change in the capacitance may be achieved by low voltage.
Patent Literature 1: JP 4502609 B1.
Patent Literature 2: JP 5000660 B1.
A variable capacitance element including a ferroelectric film has a disadvantage in that that an ESD (Electro-Static Discharge) resistance property is poor compared to an MEMS variable capacitance element or a variable capacitance element of a semiconductor, such as a variable capacitance diode.
Moreover, when the thickness of the ferroelectric film is reduced is certain designs, the control sensitivity (the ratio of a change in the capacitance value to a change in the control voltage) will be increased, but the ESD resistance property will deteriorate due to the reduction in the thickness of the ferroelectric film. That is, upon receiving an ESD that exceeds the ESD resistance property, the surge is applied to the ferroelectric film causing the ferroelectric film to break down. Accordingly, there is a restriction in reducing the thickness of the ferroelectric film from the standpoint of the ESD resistance, and the control sensitivity is also restricted.